1. Technical Field
The present invention relates to a process for manufacturing dies for pasta, the dies themselves, and their use in the production of pasta.
2. Description of Related Art
U.S. Pat. No. 3,008,434 (Maldari), filed on Feb. 3, 1960, aims to provide a generic die for different types of finished products such as pasta, bread sticks, cookies and bakery products, chocolate, candy and other extrudable materials. According to Maldari the die must be able to stand up under long continued use and maintain its proper dimensions under such extended use. The die described by Maldari comprises a holding cup having a circular side wall and a rigid flat bottom wall, a flat disk of Teflon sited on said flat bottom wall in close fitting engagement with said circular side wall and a flat rigid top plate in flat engagement with the upper surface of said disk. The disk of Teflon is held sandwiched between the rigid bottom wall and the rigid upper plate. The top plate, the disk of Teflon and the bottom wall have coaxial extrusion openings, which are respectively downwards flared in the top plate, substantially constant in the disk of Teflon and diverging downwards in the bottom wall. Therefore, the shape of the extrusion passage is convergent/constant/divergent and is the only one claimed by the patent. However, in the description of Maldari, column 2, lines 48-56, one can read that “the holder, which is usually of brass or bronze, may in some instances, as in the illustrated construction, be made to closely match or possibly decrease the size of the die outlet or outlets in the Teflon disk, thus to make the outlet 16 form a gage determining the size of the extruded product and creating a stronger, more compact than if it were extruded simply through the Teflon.”
Except that in this passage, Maldari refers only to the introduction of Teflon in a die and gives no indication about the advantages of the combined use of bronze and Teflon in optimizing extrusion of products in general and pasta in particular. In fact, the statement quoted above, which is not reflected either in the claim or in the drawings of the patent, is not even proven by the evolution of the art after the Maldari patent until now. In fact, as well known with particular reference to the pasta, in order to obtain a compact and strong product, it is requested to extrude only through Teflon that is more capable of withstanding high pressures than bronze. On the contrary bronze, in which friction is increased, consequently increases the extrusion temperature which may damage the protein fraction contained in the semolina flour with a result of compromising finished product quality (Walsh et al, 1971; Abecassis et al, 1994).
U.S. Pat. No. 5,089,284 (Irvin) discloses a method of forming pasta through an extruder that is equipped with a die plate having a plurality of holes whose transversal cross-sections decrease in the direction of extrusion. A dough as a mixture of flour rich in gluten and water is extruded through the die plate so that the extruded pasta remains substantially uncooked, i.e. a major portion, greater than about 80 percent by weight of the total starch content, is ungelatinized (i.e., less than about 20 percent gelatinization). Irvin claims heating the die plate to a temperature of at least about 54 degrees Celsius, the die plate having frustoconically shaped holes that are coated with plastic material with a low coefficient of friction until the cross-section of the hole with its smallest value. The shape of the extrusion passage of the die is then frustoconical-cylindrical. It is clear that the aim of Irvin is to leave the surface of the last section of the die orifices not covered with plastic only for allowing the dough to be extruded with direct thermal contact with the die being heated only in the last section, in order to restrict the gelatinization to the outermost “corona” region of the shape. Then Teflon acts as a partial thermal insulator (description of Irvin, column 8, lines 30-52).
U.S. Pat. No. 6,413,565 (Debbouz) aims to provide a superficially not rough pasta with improved organoleptic qualities. Said pasta is obtained by a process of extrusion through a die comprising a plurality of flow passages completely coated with a material with a low coefficient of friction, which for convenience is indicated by way of example as polytetrafluoroethylene or PTFE, commercially known as Teflon by DuPont.
To date, in both industrial and artisanal pasta production provision is made that two materials are used in contact with the product being extruded in the terminal step of extrusion:                only Teflon extruding surface;        only bronze extruding surface.        
In the following strengths and weaknesses related to the exclusive use of either material are described. Then, the present invention will be disclosed that, by combining Teflon and bronze in sequence within each singular die in the extruding surface, achieves a prefixed object.
Strengths of the use of Teflon in the extrusion with respect to bronze:                Teflon gives the pasta a smooth and shiny appearance and prevents heat stress to the product, thanks to less friction, thus enhancing also raw materials used;        the resulting pasta has higher toughness and more chewing resistance;        Teflon allows higher speed of work and higher resistance to pressure;        less wear.        
Weaknesses of the use of Teflon in the extrusion with respect to bronze:                industrial perception of the final color of the product;        greater appearance of small imperfections in the product (white and black dots etc.).        greater appearance of any difference in color (lighter or darker);        less enhanced sauces;        
Strengths of the use of bronze in the extrusion with respect to Teflon:                pasta takes on a roughness and a porosity that allow pasta to retain sauces at the best and enhance flavors;        more artisanal appearance of the product that is appreciated by consumers.        
Weaknesses of the use of bronze in the extrusion with respect to Teflon:                pasta has less toughness and lower chewing resistance;        high friction during extrusion and greater risk of thermal damage of the raw material used, starch gelatinization, protein denaturation (Dexter et al, 1971);        excessive release of dust in suspension, in both pasta production step and packaging step, which can gives rise to insect problems.        